Results of the recent Merck Ad5 vaccine trial suggest that our current understanding of protective immunity in HIV infection is severely limited. As increasing evidence indicates that the early events in HIV infection determine the long-term outcome of this disease, integrated studies of acute HIV pathogenesis are warranted to identify the critical components of innate and adaptive immunity that ultimately impact viral control. While current HIV vaccine design strategies focus on inducing stronger and broader T cell responses, little consideration has been directed towards the selection of specific vaccine antigens and the quality of the antiviral immune response. We hypothesize that current vaccine approaches are not sufficiently focused with respect to antigen selection to induce the most protective and functional early T cell responses against the most critical regions of the virus, and that far more concerted efforts, both immunologically and virologically, is necessary to identify these critical regions. This Program Project Grant (PPG) represents an outgrowth of a long and productive effort to understand the immunologic and virologic events related to acute infection. During the previous period of support through the AIEDRP, we established an extensive cohort of persons with acute infection and identified key insights into the immunology and virology of acute infection. Here we propose to build upon this work to identify factors that we believe are fundamental to a protective antiviral immune response, including regions of HIV: (1) that are immunodominantly targeted by CD8+ T cell responses during acute HIV infection that exhibit strong antiviral activity. (2) that are rapidly processed into epitopes and presented by HLA alleles. (3) that are refractory to viral escape, or escape only at the cost to replicative fitness: and (4) that preferentially bind to stimulatory mvelomonocvtic receptors on myeloid dendritic cells. We believe that these vulnerable regions of HIV need to be identified to allow for the rational selection of specific antigenic regions for inclusion into a vaccine. In addition, it will be critical to determine how to best focus the vaccine-induced immune response against these regions, which will require an understanding of (5) what types of innate responses correlate with the induction of adaptive T cell responses with strong antiviral activity, and (6) what modifications to flanking regions of epitopes will enhance the antigen processing and presentation of the critical regions of HIV. This PPG application will provide highly relevant data for vaccine design regarding the earliest protective innate and adaptive immune responses, the parameters that define effective functional immune responses, and how these shape viral evolution and viral fitness.